1. Field of the Invention
The present invention relates to a perpendicular magnetic recording medium including a magnetic film suitable to high-density magnetic recording.
2. Description of the Related Art
With a recent increase in computer's processing speed, a magnetic storage device (HDD) for recording and reproducing information is required to have high speed and high density. The most popular HDD recording system at present is a longitudinal recording system in which magnetization lies in the longitudinal direction of a medium. To further increase the density, however, perpendicular magnetic recording is preferred because a demagnetizing field near the magnetization reversal boundary is small and sharp reversal magnetization is obtained. Also, thermal fluctuation, which is a problem in magnetic recording media in recent years, can be suppressed by the perpendicular medium since the film thickness of perpendicular medium can be made larger than that of longitudinal medium.
Conventionally, CoCr-based disordered alloys such as CoCrPt have been mainly studied as the material of a perpendicular magnetic film. However, since thermal fluctuation can become a future problem even in perpendicular media, a material having higher perpendicular magnetic anisotropy than those of the conventional CoCr-based materials is necessary. As promising candidates of the material, research is being extensively made on an ordered alloy in which an ordered phase is formed by a magnetic material selected from Fe, Co and Ni and a noble metal element selected from Pt, Pd, Au and Ir. In particular, FePt and CoPt as ordered alloys having an L10 crystal structure have high magnetic anisotropies of 7×107 and 4×107 erg/cc, respectively, in the c-axis direction (<100> direction). Therefore, a perpendicular medium having a high thermal fluctuation resistance can be formed when one of these materials is used for a recording layer. Unfortunately, to use these materials as a perpendicular magnetization film, the c-axis as the easy axis of magnetization must be oriented perpendicularly to the film surface.
The following techniques are conventionally known as methods of forming a c-axis oriented film. For example, Jpn. Pat. Appln. KOKAI Publication No. 2001-189010 discloses a technique in which at least one (100)-oriented underlayer is formed between a substrate and magnetic layer. Also, Jpn. Pat. Appln. KOKAI Publication No. 11-353648 discloses a technique in which a Cr alloy underlayer containing Cr and Ti or the like is formed. Relatively good perpendicular magnetization films are obtained by this technique.
To allow an ordered alloy to achieve high magnetic anisotropy, however, it is generally necessary to be annealed at several hundred degrees during or after film deposition. This annealing increases the size of crystal grains and hence increases the magnetic cluster size, thereby making it difficult to improve recording resolution.
Accordingly, to realize a high-density perpendicular magnetic recording medium using an ordered alloy as a recording layer, it is necessary to decrease the magnetic cluster size by decreasing the crystal grain size or magnetically isolating the crystal grains in the recording layer, in addition to improving the c-axis orientation.
To magnetically isolate the crystal grains in an ordered alloy, an attempt to add a nonmagnetic element such as MgO to an ordered alloy magnetic layer has been disclosed in, for example, IEEE Transactions on Magnetics, vol. 37, No. 4, pp. 1283–1285. However, this technique is not enough to magnetically isolate magnetic grains. In addition, to order this ordered alloy, annealing at 500° C. or more after film deposition or substrate heating during film deposition is necessitated, which lowers productivity.